Per(halo-oxygen) acid oxidation,purification and recovery process and apparatus therefor

ABSTRACT

AN ELECTRODIALYTIC APPARATUS UTILIZING ANION AND CATION PERMSELECTIVE MEMBRANES AND HAVING AT LEAST ONE TWOCHAMBER CELL FOR PURIFICATION AND AT LEAST ONE THREE-CHAMBER CELL PROXIMAL THE TWO-CHAMBER UNIT FOR CONCENTRATION OF AQUEOUS PER(HALO-OXYGEN) ACIDS AND THEIR SALTS, ALL ANOLYTE CHAMBERS SHARING A COMMON ANOLYTE STREAM, ALL CATHOLYTE CHAMBERS SHARING A COMMON CATHOLYTE STREAM, AND AT LEAST ONE OF THE ANOLYTE CHAMBERS OF THE PURIFICATION AND THE CONCENTRATION CELLS SHARING A COMMON ANODE. A MULTI-STEP PROCESS FOR RECOVERING AND REGENERATING THE PERIODATE OXIDANT USED IN PREPARING OXIDIZED POLYSACCHARIDES IN WHICH THE PRIMARY LIQUOR AND SUBSEQUENT WASH LIQUORS FROM THE OXIDIZED POLYSACCHARIDE FILTER CAKE ARE CIRCULATED IN THE ANOLYTE AND MIDDLE CHAMBERS OF THE ELECTRODIALYTIC APPARATUS HAVING TWO-CHAMBER AND THREECHAMBER CELLS FOR RE-OXIDATION AND CONCENTRATION RESPECTIVELY, THE LIQUORS HAVING A CONCENTRATION OF 4 TO 15 WEIGHT PERCENT BEING CIRCULATED IN THE ANOLYTE CHAMBERS; THOSE LIQUORS HAVING A CONCENTRATION OF 0.5 TO 5 WEIGHT PERCENT BEING CIRCULATED IN THE MIDDLE CHAMBER, ALL LIQUORS AND EFFLUENTS HAVING A CONCENTRATION OF LESS THAN 0.5 WEIGHT PERCENT BEING PASSED THROUGH A STRONG BASE ANION EXCHANGE RESIN WHICH REMOVES THE REMAINING PERIODATE, OR CHEMICALLY REDUCED PERIODATES, WHICH ARE SUBSEQUENTLY ELUTED BY THE SODIUM HYDROXIDE CATHOLYTE, WHICH IN TURN IS CIRCULATED IN THE ANOLYTE CHAMBERS OF THE APPARAUS FOR REGENERATION.

NOV. 21, 1972 A, H, HElT EI'AL Mmmm-OXYGEN) ACID OXIDATION,

3,703,508 PURIFICATION AND RECOVERY PROCESS AND APPARATUS THEREFOR Original Filed April 8, 1968 2 Sheets-Sheet 1 A. H. HEIT ErAL 3,703,508

2 Sheets-Sheet 2 PEH(HALOOXYGEN) ACID OXIDATION, PURIFICATION AND RECOVERY PROCESS AND APPARATUS THEREFOR Nov. 21, 1972 Original Filed April 8, 1968 United States Patent O PERGIALO-OXYGEN) ACID OXIDATION, PURI- FICATION AND RECOVERY PROCESS AND APPARATUS THEREFOR Allyn Harold Heit, Mount Holly, and James Norris Willlamson, Marlton, NJ., assignors to Syhron Corporation, Rochester, N.Y.

Original application Apr. 8, 1968, Ser. No. 719,361, now Patent No. 3,607,694, dated Sept. 21, 1971. Divided and this application Oct. 7, 1970, Ser. No. 78,992

Int. Cl. C08b 15/00 U.S. Cl. 260-212 1 Claim ABSTRACT OF THE DISCLOSURE An electrodialytic apparatus utilizing anion and cation permselective membranes and having at least one twochamber cell for purification and at least one three-chamber cell proximal the two-chamber unit for concentration of aqueous per(halooxygen) acids and theirsalts, all anolyte chambers sharing a common anolyte stream, all catholyte chambers sharing a common catholyte stream, and at least one of the anolyte chambers of the purification and the concentration cells sharing a common anode. A multi-step process for recovering and regenerating the periodate oxidant used in preparing oxidized polysaccharides in which the primary liquor and subsequent wash liquors from the oxidized polysaccharide lter cake are circulated in the anolyte and middle chambers of the electrodialytic apparatus having two-chamber and threechamber cells for re-oxidation and concentration respectively, the liquors having a concentration of 4 to 15 weight percent being circulated in the anolyte chambers; those liquors having a concentration of 0.5 to 5 weight percent being circulated in the middle chamber, all liquors and effluents having a concentration of less than 0.5 weight percent being passed through a strong base anion exchange resin which removes the remaining periodate or chemically reduced periodates, which are subsequently eluted by the sodium hydroxide catholyte, which in turn is circulated in the anolyte chambers of the apparatus for regeneration.

CROSS-REFERENCES TO RELATED APPLICATIONS This is a division of application Ser. No. 719,361, tiled Apr. 8, 1968 now Pat. No. 3,607,694.

This invention relates generally to a process for the electrolytic recovery and regeneration of inorganic halogen acids and their salts and an apparatus therefor. More particularly it relates to a method for the electrodialytic recovery, and regeneration of periodic acid and its salts, and re-use of the periodic acid and its salts in the oxidation of polysaccharides.

The Malaprade reaction is an illustration of the application of periodic acid and its salts in organic oxidations. This reaction consists in the treatment of an organic material having vicinal hydroxy groups with either periodic acid or an alkali metal periodate resulting (a) in the conversion of the vicinal hydroxy groups to aldehyde and (b) in the conversion of the periodic acid or the periodate salt to a chemically reduced form such as, iodic acid or its salts. The reaction may be shown as:

r' ICC where (1) represents the vicinal hydroxy groups such as those found in starch or cellulose, (2) represents the aldehyde group and (3) represents the chemically reduced periodic acid or periodate. A typical Malaprade reaction may be illustrated by the conversion of starch regardless of vegetable origin, to so-called dialdehyde starch as represented by (2) in the above reaction. The starches and celluloses so treated are members of the class designated as polysaccharides, and the products, polysaccharides oxidized by periodic acid and its salts, may be referred to as oxidized polysaccharides.

The production of dialdehyde starch and other oxidized polysaccharides has attained commercial status, and due to the expense involved in the use of the expense periodic acid and its salts as oxidants, and the need for a more eicient and economical process for the production of the oxidized polysaccharides has arisen. Public concern and legislation also require the development of methods resulting in the absence of contamination and pollution of rivers, lakes, underground water tables and the like, from the discharge of process euents. Several methods, both electrolytic and chemical and combinations thereof, have been developed for the production of dialdehyde starch and other oxidized polysaccharides; however, none of these electrolytic methods are economically capable of any more than oxidation of chemically reduced periodic acid or its salts present in liquors in excess of 4 weight percent of the periodic acid or its salts. It is therefore the primary object of this invention to provide an electrolytic apparatus in which chemically reduced oxidants in the form of inorganic ion dissociable materials may be electrolytically oxidized simultaneously With the electrolytic concentration of the oxidants and chemically reduced oxidants.

It has been shown in U.S. 2,648,629 and U .S. 2,713,553 that polysaccharide materials can be oxidized in a twochamber electrolytic cell in which periodic acid is formed and simultaneously consumed by the starch. It has also been demonstrated in U.S. 2,830,941 that alkali metal periodate can' be prepared electrolytically by a separate unit operation thereby eliminating the various complications attending the maintenance of a starch-iodate slurry within the electrolytic cell. U.S. 2,648,629, U.S. 2,713,553 and U.S. 3,131,137 set forth design parameters of twochamber periodate cells. The electrolytic cells which are used in connection with the oxidation of polysaccharides and are disclosed in the prior art in general share the following features: (1) Open-cell structure, (2) use of alundum thimbles as barriers between catholyte and anolyte chambers, (3) planar rectangular or cylindrical lead anodes, (4) rod or tube steel cathodes and (5) circulation of anolyte by agitator action or pumping from a reservoir.

An electrolytic cell having multiples of a two-chamber unit has been disclosed in Industrial and Engineering Chemistry, Process Design and Development, vol. l, page 144 (1962). Each two-chamber unit has an anolyte chamber and a catholyte chamber separated by a diaphragm. Using iodic acid as anolyte and sodium hydroxide as catholyte, periodic acid can be formed at the anode when a potential difference is applied across the electrodes. In a typical example using this prior art multiple unit electrolytic cell a starch slurry (not within the cell) is iirst oxidized to dialdehyde starch by means of a periodic acid solution. A iilter cake of the oxidized starch is separated from the slurry, and the acidic iodate-rich liquor obtained after separation is cycled through an evaporator where much o f the water is removed. The acidic iodate-rich 3 liquor concentrated by evaporation is circulated in the anolyte chamber of the electrolytic cell where the periodic acid is regenerated at the anode. A 5% sodium hydroxide catholyte solution is used in the catholyte chamber of the cell. Small quantities of the catholyte solution are added to the anolyte solution to maintain the pH as required.

These prior art electrolytic cells and processes suffer from several major deficiencies, which in the main, have prevented their commercial acceptance. Among them is the fact that no provision is made for handling the dilute wash waters and other eliiuents which contain about 0.01 to 4.0 weight percent of periodic acid, and its salts and chemically reduced periodic acid and its salts except for a separate concentrating by iiash evaporation. As a practical matter recovery is generally postulated on only 8 to 10 weight percent iodate liquors in the prior art processes.

Evaporation is unavoidably limited to the stronger concentrations of the dilute wash waters by reason of the economics of evaporation techniques. The presence of heat in such evaporation techniques leads to the decomposition of the acidic solutions of iodine-containing acids and their salts through interaction with various organic materials, such as oils, fats, protein residues and water soluble extracts, leached into the slurries and liquors from the polysaccharides under treatment or formed from the polysaccharides by a hydrolytic or oxidative degradation of the starch. Therefore, it is a object of this invention to provide a process for the oxidation of polysaccharides in which all periodic acid and its salts and chemically reduced periodic acid and its salts present in wash waters and liquors are recovered and regenerated without resorting to destructive evaporation techniques.

The prior art electrolytic cells and processes suffer from other disadvantages which include a limitation upon current densities due to inadequate electrolyte circulation rates of aqueous solutions of periodic acid and its salts; no provision for the circulation of catholyte except by periodic semi-manual emptying of reservoirs when the concentration of caustic becomes excessive; and partial utilization of the lead anode surfaces. Therefore, it is an object of this invention to provide an electrolytic apparatus for the purification and concentration of inorganic ion dissociable materials in which anolyte and catholyte are continuously circulated in a closed system and the surfaces of the lead anodes are completely utilized,

Another object of this invention is to provide a process for the removal of substantially all periodic acid and its salts and chemically reduced periodic acid and its salts from oxidized polysaccharide wash waters, liquors and effluents which are recycled for use as wash water 0r discarded. Other objects will become evident to` those skilled in the art from a reading of this specification and the appended claims and drawings.

We have found that the objects of this invention can be carried out by the construction and operation of single electrodialytic apparatus consisting of two sections, one section having a two-chamber unit designated as a purification cell or multiples thereof and the other section having a three-chamber unit designated as a concentration cell or multiples thereof. The purification and concentration sections are physically integrated into a unit construction in such a manner that the purification section or multiples thereof are proximal the concentration section or multiples thereof within a single frame. Both the purification and concentration sections derive current from a common direct current power source, derive catholyte from a common closed catholyte circulating system and derive anolyte from a common closed anolyte circulating system. The purification section of the electrolytic apparatus consists of at least one two-chamber arrangement characterized by an anolytic chamber, an anode having a surface in the anolyte chamber in contact with the anolyte, a catholyte chamber, a cathode having a surface in the anolyte chamber in contact with the catholyte, and a cation permselective membrane separating the chambers, one surface of which serves as a barrier for the anolyte chamber and the other surface of which serves as a barrier for the catholyte chamber, all elements being mounted within a suitable frame.

The concentration section mounted proximal to the purification section within the same suitable frame, consists `of at least one three-chamber arrangement characterized by an anolyte chamber, an anode having a surface in the anolyte chamber in contact with the anolyte, a middle chamber, an anion permselective membrane separating the anolyte chamber from the middle chamber, a catholyte chamber, a cathode having a surface in the catholyte chamber in contact with the catholyte and a permselective membrane separating the catholyte chamber from the middle chamber. All membranes serve as barriers for the chambers which they separate. The permselective membrane utilized to separate the catholyte chamber from the middle chamber may be either an anion permselective membrane or a cation permselective membrane. All anolyte chambers in the purification section of the apparatus are connected by pipe or suitable conduit to all anolyte chambers in the concentration section and share a common anolyte reservoir. All catholyte chambers in the purification section of the apparatus are connected by pipe or suitable conduit to all catholyte chambers in the concentration section and share a common catholyte reservoir.

The preferred multiple-cell purification section is constructed in such a manner that there is maximum utilization of the anode surface. Thus, one anode may serve as the anode for two anolyte chambers. 'In the preferred multiple-cell purification section one catholyte chamber and its circulating stream of catholyte liquor serves two anolyte chambers and streams, one of the anolyte chambers being located on one side of the catholyte chamber and the other located on the opposite side of the catholyte chamber with necessary permselective membranes and other required elements inserted therebetween.

The preferred multiple-cell concentration section is constructed in such a manner that there is maximum utilization of the anode surface. Thus, one anode serves as the anode for two anolyte chambers. In the preferred multiplecell embodiment one catholyte chamber and its circulating stream in the concentration section serves two middle chambers and streams. yIn the preferred embodiment of the apparatus having a concentration section and a purification system, at least one of the anolyte chambers of a concentration section and the purification section share a common anode. However, cell construction may be varied to permit a chamber arrangement in which at least one catholyte chamber of the purification section and at least one catholyte chamber of the concentration section share a common anode. Although the preferred cell arrangement is designated above, we do not intend to limit the unit construction and the general plan of anolyte and catholyte systems common to both purification and concentration systems to any specific arrangement of electrolyte chambers, electrodes and the like.

The function of the purification section of the electrolytic apparatus is the regeneration of chemically reduced inorganic per(halooxygen) acids and their salts at the anode and the removal of cations from the anolyte liquor. Such chemically reduced inorganic per(halooxy gen) acids and their salts which may be regenerated in the anolyte chambers include chemically reduced periodic acid, sodium periodate, perchloric acid, sodium perchlorate, ammonium perchlorate or mixtures of such iodates, chlorates, periodates and perchlorates combined with such cations at Na+, H+, NH4+. The oxygen required for the necessary regeneration is generated by the electrolytic decomposition of water at the anode. Thus, iodide anion will be oxidized to iodate anion which will be further oxidized to periodate anion at the anode. This oxidation process at the anode is accompanied by a simultaneous migration or cations across the cation permselective membrane separating the anolyte and catholyte chambers from the anolyte to the caustic catholyte liquor. In this way undesirable cations, such as, sodium, ammonium and the like may be removed from the anolyte liquor, hence the designation of this section or cell as the puriiication section. The preferred caustic catholyte liquor is a aqueous solution of sodium hydroxide. Hydroxide anion is generated by the electrolytic decomposition of water at the cathode, however, the cation permselective membrane prevents the migration of the cations to the anode resulting in ya net increase in caustic concentration of the catholyte liquor due to the presence of the migrant cations and the retained hydroxide anions.

The primary function of the three-chamber or concentration section of the electrolytic apparatus is the concentration of inorganic per(halooxygen) anions and their chemically reduced derivatives including iodate, chlorate, iodide and chloride. These per(halo-oxygen) anions may be paired with a cation or a combination of such cations as sodium cation, ammonium anion and hydrogen. The periodate, `iodate and like anions initially in the middle chamber and designated as dialysate, migrate from the middle chamber toward the anode through the anion permselective membrane into the anolyte. Concurrently with the concentrating function the anolyte chamber also functions in the oxidative regeneration of the chemically reduced per(halooxygen) anions and their salts in the same way that the anolyte chamber of `the purification section regenerates the chemically reduced acids and their salts. Since an anion permselective membrane is used between the anolyte and middle chambers, anions are permitted to pass from the middle chamber to the anolyte chamber while cations are prohibited from migrating from the anolyte chamber to the middle chamber. The iodateperiodate or other per(halooxygen) anions or their chemically reduced derivatives which migrate from the middle stream are replaced predominantly by hydroxyl anions migrating toward the anode from the catholyte chamber when the permselective membrane between the catholyte and middle chambers is an anion permselective memberane. By this mechanism the anolyte liquor becomes enriched with the iodate, periodate or any other [halogen anion derivative which may be present, while the middle chamber electrolyte (dialysate), subsequently destined for waste or further treatment by an anion exchange resin bed, is depleted in iodate, periodate and other halogen anion derivatives.

A cation permselective membrane may also be used between the catholyte and middle chambers. When this arrangement is used the cations present in the dialysate circulating in the middle chamber migrate toward the cathode through the cation permselective membrane into the catholyte liquor where they unite with the hydroxyl ion retained in the catholyte liquor by reason of the cation permselective barrier. The dialysate circulated in the middle chamber may lbe an aqueous solution of per- (halo-oxygen) acids and their salts and chemically re duced derivatives thereof.

Suitable anion and cation exchange membranes which must remain stable for long periods of exposure to the corrosive ,action of the liquid media used as circulating liquors, were used in the electrodialytic apparatus. The Ionac Chemical Company 3400 series permselective membranes have proven sufficiently durable to withstand such corrosivity and may be used in the apparatus of this invention.

The electrodialytic cell of this invention is constructed in such a way that the entire system including all chambers, electrodes and circulating systems can operate simultaneously at full efficiency. Any individual section or unit of the electrodialytic apparatus may be disengaged from p operation while other sections or units of the cell con` tinue to operate eciently. This can be accomplished by 6 merely obstructing fthe circulating stream to 'any individual chamber or section.

The anodes used in the electrodialytic cell of this invention are preferably of a silver-lead alloy containing ap proximately 1% silver. Both sides of each lead anode plate are used to supply current to an anolyte chamber in the preferred embodiment of this invention. Thus, a typical purification section in a multiple-cell arrangement may have the following series of elements: an anolyte chamber at the end of the unit, then a catholyte chamber, an anolyte chamber, an anolyte chamber, a catholyte chamber and the like. A typical concentration section in a multiple-cell arrangement may have the following series of elements; a catholyte chamber, middle chamber, anolyte chamber, anolyte chamber, middle chamber, catholyte chamber and the like. Terminal anolyte chambers are served by a single anode and terminal catholyte chambers serve a single anolyte chamber in the preferred embodiment.

During the operation of the electrolytic apparatus the effective difference in potential is considered to be that amount of current which will cause (a) the migration of a suiiicient number of anions and cations to substantially vary the concentrations of the liquors within the chambers in a designated interval of time and (b) the oxidation or regeneration of a substantial number of the chemically reduced inorganic anions Within a designated interval of time.

In relation to the electrolytic apparatus of this invention we have also found a process for quantitatively recovering and regenerating the periodate oxidant used in preparing oxidized polysaccharides. The irst step in this process is the separation, water washing and drying of oxidized polysaccharides in successive steps to form a solid product and as many aqueous liquors as necessary to substantially remove all periodate and chemically reduced periodate anions from the solid filter cake by successive water washings.

In the preferred embodiment of the process for oxidizing polysaccharides the primary liquor obtained from the filtration of the motor liquor from the oxidized polysaccharide has a periodate and chemically reduced periodate anion concentration of about 4 to 15 weight percent. Washing of the Ililter cake with either de-ionized water or Water from which all periodate and chemically reduced periodate anions have been removed and hereafter designated as de-anionized water, produces a secondary liquor having from about 1 to 8 Weight percent of periodate and chemically reduced periodate anions. Subsequent washings of the lter cake as above produce a tertiary liquor having from about 0.5 to 5 weight percent of periodate and chemically reduced periodate anions and a quaternary liquor having from about 0.01 to 0.5 weight percent of periodate and chemically reduced periodate anions. Each of these liquors may be subsequently concentrated to about 5 to 15 Weight percent of periodate and chemically reduced periodate anions, and the chemically reduced periodate anions may be oxidized to periodate anions for re-use in oxidizing polysaccharides.

All of the aqueous periodate and chemically reduced periodate anions present in the liquors obtained from the filtering and washing of the ilter cake in which the concentration of the periodate and chemically reduced periodate anion concentration is in excess of about 0.5 weight percent, may be concentrated to about 5 to 15 weight percent by circulating the liquor in the middle chamber of the concentration cell set out above. All aqueous periodate and chemically reduced periodate anions present in the liquors obtained from the washing and filtering of the filter cake in which the concentration of the periodate and chemically reduced periodate anion concentration is less than about 0.5 weight percent, may be concentrated by ion accumulation on an anion exchange resin. The anions accumulated on the anion exchange resin may be eluted from the resin by using an aqueous caustic solution and in the preferred embodiment may be eluted by the caustic catholytic liquor from the electrolytic apparatus discussed above. The eluate may then be circulated in the anolyte chamber of the electrolytic apparatus where the chemically reduced periodate anions, such as, sodium iodate, will be oxidized to the periodate anion. All references to periodate anions refer to periodic acid as well as to its sodium and other salts.

All chemically reduced periodate anions are circulated in the anlyte chamber of the electrodialytic apparatus to convert the chemically reduced periodate anion to the periodate anion.

When the aqueous liquors having from about 0.5 to weight percent of periodate and chemically reduced periodate anions are circulated in the middle chamber of the electrolytic apparatus, the periodate and chemically reduced periodate anions migrate across the anion permselective membrane to the anolyte chamber to provide an aqueous solution in the anolyte chamber of about 5 to weight percent periodate and chemically reduced periodate anions. The chemically reduced periodate anions which have migrated to the anolyte chamber of the concentration section, are then oxidized to periodate anions in the anolyte chambers of both the concentration and purification sections. The middle chamber effluent which may be designated as a quinary liquor, contains about 0.01 to 0.5 weight percent periodate and chemically reduced periodate and is passed through the anion exchange resin to remove substantially all traces of the periodate and chemically reduced periodate anions. The same ion exchange resin bed may be used to remove periodate and chemically reduced periodate from the quaternary and quinary liquors. The effluent from the anion exchange resin bed is completely de-anionized. By de-anionized we mean that all periodate and chemically reduced periodate anions are removed from the efiiuent.

A suitable ion exchange resin for the removal of the periodate and chemically reduced periodate anions is a strong base polystyrene alkyl quaternary ammonium ion exchange resin the sulfate form manufactured by Ionac Chemical Company as Ionac A-540. This ion exchange resin insures complete removal of all traces of iodine, iodic acid, periodic acid and their salts from the eiuent Water which may be utilized in subsequent washing of oxidized polysaccharide filter cakes or may be discarded as waste.

A complete understanding of the invention may be obtained from the following description and explanation which refer to the accompanying drawings illustrating an embodiment directed in the recovery and regeneration of periodic acid and its salts and chemically reduced derivatives thereof.

FIG. 1 is a diagrammatic representation of a process for oxidizing polysaccharides and recovering and regenerating the periodate oxidant used in oxidizing the poly saccharide.

FIG. 2 is a diagrammatic representation of a longitudinal cross-section of an electrolytic cell.

Referring to FIG. 1, a polysaccharide and anolyte from the stream designated as 19d containing regenerated periodic acid and its salts in a concentration of about 5-15 weight percent taken from anolyte reservoir R-11, are reacted in an ordinary reactor. The resulting oxidized polysaccharide slurry is filtered at filter step 1 resulting in the separation of the primary liquor from the primary wet solids. The primary liquor, which contains less than 5-15 weight percent of unreacted periodic acid land its salts and chemically reduced periodic acid and its salts, is returned to reservoir R-11 by conduit 19a for subsequent re-oxidation in the anolyte chambers 11a and 11b of the electrolytic apparatus.

The primary wet solids are then Washed or slurried with de-anionized water-1, which may be completely deionized water or water in which periodate and chemically reduced periodate anions have been removed, to form mixture 1. Mixture 1 is filtered at filter step 2 resulting in the separation of secondary wet solids and secondary liquor. The secondary liquor containing about l to 8 weight percent periodate and chemically reduced periodate is added to anolyte reservoir R-11 by means of conduit 19b. Thus, the primary and secondary liquors are returned to anolyte reservoir R-11 for circulating as anolyte in the anolyte chamber and subsequent re-oxidation in anolyte chambers 11a and 11b of the electrolytic apparatus.

The secondary wet solids are washed or slurried with de-anionized water-2 to form mixture 2. Mixture 2 is filtered by standard filtration techniques in filter step 3 to provide a tertiary liquor and tertiary wet solids. The tertiary liquor having a periodate and chemically reduced periodate concentration of about 0.5 to 5 weight percent passes to middle chamber reservoir R-12 by means of lconduit 20a to become the liquor designated as dialysate or electrodialysate. The dialysate is circulated by means of conduit 20 to, through and from the middle chamber 12 of the resin bed where the periodate anions are accumulated on the anion exchange resin, Iand the efiiuent the electrolytic apparatus. When the concentration of the dialysate in reservoir R-12 reaches about 0.01 to 0.5 weight percent of periodate and chemically reduced periodate anions, the dialysate is passed to an anion exchange resin bed or column by means of conduit 20b. As the dialysate liquor passes through the anion exchange resin the periodate and chemically reduced periodate anions accumulate on the anion exchange resin, and the effluent stream, 20d, passing from the anion exchange resin bed, is designated de-anionized water-4. De-anionized Water-4 has no trace of periodate or chemically reduced periodate anions until the anion exchange resin has been exhausted and requires regeneration. However, de-anionized water-4 may contain hydroxyl anion. Deanionized water-4 may be used as wash waters designated as de-anionized water-1, -2 and 3, or it may be discarded as Waste from which all periodate and chemically reduced periodate anions have been removed. Deanionized Water-1, 2 and -3 may ybe any type of water purified by distillation or ion exchange processes.

The tertiary wet solids are Washed or slurried with deanionized water-3 to form mixture 3. Mixture 3 is filtered at filter step 4 producing a reduced periodate impoverished liquor and a wet solid product. The wet solid product is an oxidized polysaccharide which is subsequently dried to form a dry solid product useful as fabric softeners and the like. The reduced periodate impoverished liquor, the quaternary liquor has a periodate and chemically reduced periodate anion concentration of about 0.01 to 0.5 weight percent and is passed by conduit- 21 to the anion exchange recovery and regeneration designated as 2lb is added to the de-anionized water-4 in a manner similar to that explained for the dialysate dialysate efliuent which passes through conduit 20b.

The periodate and chemically reduced periodate anions which have accumulated on the anion exchange resin may be eluted from the resin by caustic catholyte from catholyte reservoir R-13. The caustic catholyte, which has a concentration of about 5 to 10 weight percent sodium hydroxide, passes by conduit 18a to the anion exchange resin. The periodate and chemically reduced periodate anions are eluted from the anion exchange resin and pass by conduit 19C to anolyte reservoir R-11 for re-oxidation of the chemically reduced periodate, and the anion exchange resin is regenerated for subsequent removal of periodate anions. An evaporator may be placed in conduit 19e to concentrate the eluate prior to addition to reservoir R-11.

Catholyte reservoir supplies catholyte to catholyte chambers 13a and 13b by means of conduit 18. The electrolytic apparatus designated in FIG. 1 is a five chamber unit in which chambers 11a, and 12 and 13a deriving electrical potential from anode 10a and cathode 14, form the concentration section of the cell. The purification section of the cell which derives electrical potential from anode b and cathode 14, is made up of chambers 13b and 11b. Anolyte chamber 11b and catholyte chamber 13b are separated by cation permselective membrane 17. Anolyte chamber 11a and middle chamber 12 are separated by anion permselective membrane b. 'Ihe anion permselective membrane 15b may be replaced -by a cation permselective membrane with no adverse effect upon the overall recovery and regeneration scheme. Anolyte chambers 11a and 11b are supplied by a common anolyte conduit 19 from anolyte reservoir R-11, both chambers being interconnected via conduit 19 and reservoir R-11. Catholyte chambers 13a and 13b are supplied by a common catholyte conduit 18 from catholyte reservoir R43 both chambers being interconnected via conduit 18 and catholyte reservoir R-13. 'Ihe liquors in the reservoirs are circulated from the reservoirs to the respective chambers and return from the chambers to the respective reservoirs.

FIG. 2 represents a cross section of a five-chambered unit in which oxidation, purification and concentration of typical periodate and chemically reduced periodate anions are depicted as simultaneously occurring in a two-chamber purification section located proximal to a threechamber concentration section. In the over-all cell construction the Ifive chambers designated as 13a, 11a, 11b, 12 and 13b are held within a single frame designated as 16. The frame, 16, may be any material capable of withstanding the corrosive action of the liquors and having suitable structural strength and rigidity to withstand mild temperature increases and the weight of the liquors and other structural components. Anolyte chambers 11a and 11b are interconnected by means of a common conduit designated as 19. Catholyte chambers 13a and 13b are interconnected by means of a common conduit designated as 18. The purification section of the cell which comprises catholyte chamber 13a and anolyte chamber 11a are supplied with direct current by cathode 14a and anode 10 respectively. Chambers 13a and 11a are separated by cation permselective membrane 17. The concentration section of the cell which comprises catholyte chamber 13b, anolyte chamber 11b and middle chamber 12 are supplied with direct current by anode 10, a surface of which defines anolyte chamber 11b, and cathode 14b, a surface lof which defines catholyte chamber 13b. 'Ihe middle chamber, 12, is defined by anion permselective membrane 15a which separates the middle chamber from the anolyte chamber, and anion permselective membrane 15b which separates the middle chamber from the catholyte chamber.

In |FIG. 2, when a caustic catholyte is circulated in catholyte chambers 13a and 13b, an aqueous anolyte containing X, X03* and X04- is circulated in anolyte chambers 11a and 11b, and an electrodialysate containing X, XO3- and X04 is circulated in middle chamber 12, where X, XO,+ and XO,- represent periodate and chemically reduced periodate anions or perchlorate and chemically reduced perchlorate anions and where all electrolytes contain cations which may be Na+ and H+, or mixtures thereof, designated as k+, the following reaction and migrations occur simultaneously when an electrical potential is applied to the anode and cathodes:

(l) X, XO3 and X04 anions migrate from the electrodialysate in chamber 12 to the anolyte in chamber 11b;

(2) k+ cation is retained by action of the anion permselective membrane in chamber 12 where it unites with 0H* anion migrating from the catholyte in chamber 13b Where it is generated;

(3) H2O and alkali metal hydroxides present in catholyte chambers 13a and 13b generate molecular hydnogen and OH- anion; the OH anion migrates from the catholyte in chamber 13b to chamber 12 through anion permselectilve membrane 15b and which is retained in chamber 13a by action of cation permselective 10 membrane 17, while the k+ formed in chambers 13a and 13b is retained by the action of the cathodes;

(4) H+ and molecular oxygen are generated in anolyte chambers 11a and 11b by electrolytic action on water at the anode; the generated oxygen in combination with the electrical charge resulting in the oxidation of all chemically reduced X04- anions to XO., anions which are shown in generation at anode 10 in chambers 11a and 11b by the electrolytic oxidation steps of (5) k+ cations are retained in chamber 11b by the action of anion permselective membrane 15a and migrate from the anolyte in chamber 11a through cation perm.- selective membrane 17 to the catholyte in 13a in the direction of cathode 14a where k+ is retained by the action of the cathode 14a.

Therefore, the chemically reduced XO.,w anions are regenerated in chambers 11a and 11b; the X, X03- and XO.; present in the dialysate in chamber 12 are concentrated by transfer to chamber 11b; and undesirable cations, k+ are removed from the anolyte in chamber 11a by transfer or migration to the catholyte in chamber 13a.

The following specific examples are provided to further illustrate the practice of this invention.

:EXAMPLE I A multi-chambered electrodialytic cell was constructed by placing a series of purification sections consisting of the following arrangement of chambers; anolyte, catholyte, anolyte, anolyte, catholyte, anolyte, anolyte, catholyte, etc, with a total of se-ven catholyte chambers, and thirteen anolyte chambers in conjunction with a series of concentration sections consisting of the following arrangement of chambers: catholyte, middle, anolyte, anolyte, middle, catholyte, middle, anolyte, etc. with a total of four anolyte chambers, three catholyte chambers and four middle chambers. The concentration and purification section chambers, cathodes and anodes were assembled within a common framework. Assembly of the apparatus was such that a maximum number of anolyte compartments utilized a minimum number of silverlead anodes. All anolyte chambers of both sections were supplied with anolyte from a common anolyte circulating system and trough. All catholyte chambers of both sections were supplied with caustic catholyte from a common catholyte circulating system and reservoir. The middle chambers of the concentration section were provided with a circulating system which circulated the middle chamber compartment electrolyte. An ion exchange column containing a highly basic anion exchange resin was provided for removal of iodine derivative residues from spent middle chamber electrolyte. Regeneration of the spent anion exchange resin was accomplished by passing the caustic catholyte through the anion exchange resin bed. Provision was made for the transfer of the eluted iodine-containing catholyte to the anolyte stream to minimize the loss of iodine or its derivatives.

Each chamber was one inch thick with minor variations due to gaskets and electrodes and defined a working Iarea of four square feet. Membranes were heterogeneous in nature and constructed on a webbing of inactive supporting fibers by means of an inert binder. In the primary section of the electrodialytic apparatus the anolyte and catholyte compartments were separated by cation permselective membranes. Anion permselective membranes were used between the anolyte and middle chambers and catholyte and middle chambers of the concentration section. Ionac Chemical Company 3400 series of membranes which have proven stable for long periods of exposure to the corrosive action of the liquid media used in the circulating streams, were used in the electrodialytic apparatus. Anodes were formed from a lead alloy comprising about 1% silver, and the perforated cathode was formed from a mild steel.

The catholyte was a 5% sodium hydroxide solution. The anolyte was the primary filtrate from a periodic acid oxidation of starch for the production of dialdehyde starch and consisted of unreacted periodate and iodate anions. The iodate was present from the reduction of periodate during the polysaccharide oxidation. The solution in the middle compartments of the concentration section consisted of the dilute iodate-periodate-containing washings from the dialdehyde starch filter cake.

Anolyte, 85 gallons, with a total iodate-periodate concentration (calculated as periodate) of 83.2 Ignams/liter was circulated through the anolyte system common to both the purification and concentration sections. The actual periodate concentration of the anolyte was 64.0 grams/ liter. Therefore, 77.0% of the anolyte was periodic acid. The 5% NaOH catholyte was circulated through the catholyte system common to both sections. A volume of 70 gallons of dilute wash water was circulated through the middle chamber of the concentration section. The total iodine content of the dilute wash water was 9.9 grams/liter (calculated as periodate).

Voltage was applied at the electrodes by means of a rectifier, and the current of the system was maintained at approximately 1200 amps. The temperature was normally 35-40 C.

The table following shows the results of the electrodialytic regeneration and concentration. The column represented as Total under Middle represents the total concentration of iodate and periodate (calculated as periodate) in grams/liter in the middle compartment of the concentration section.

The table shows that the concentration of periodate and percent periodate increases with time, indicative of regeneration of periodate from iodate in the liquor. The total concentration of the iodate-periodate liquor in the middle compartment decreases with time indicative of removal of the iodine derivatives from the middle stream.

The dilute wash waters were cycled through the middle chamber of the concentration section until the iodate concentration of the middle stream was 1.5 g./l. The 70 gallons of liquor in the middle stream was then cycled through anion exchange column consisting of 1.5 cu. ft. of strong base polystyrene lalkyl quatern'ary ammonium ion exchange resin in the sulfate form, manufactured by Ionac Chemical Company as Ionac A-540. The eluted liquor contained no trace of iodine or its derivatives and was discharged 'into the sewer.

The strong base ion exchange resin was exhausted after eluting several other cycles iodate-containing liquor through the column. Exhaustion of the resin can be determined by the presence of iodate in the eluted liquor. The ion exchange resin was then regenerated by passing the caustic catholyte from the catholyte circulating system through the resin bed. The eluted liquor was added to the anolyte system for regeneration.

EXAMPLE II In an electrodialytic regeneration and concentration of the ltnates from `a periodic acid conversion of cellulose to dialdehyde cellulose the same lapparatus, method and quantities were used as given in Example I. The following table showing the total concentration of iodate periodate in grams/liter in the anolyte and middle streams and the concentration and percent periodate in the anolyte 12 in relation to length of time of operation of the apparatus at a current of 1200 amps input is given below.

It can be seen from examination of the data that the percentage of periodate in the anolyte increases with time. Note that within 11.5 hours the periodate concentration of the anolyte more than doubled. The total concentration of the iodate periodate in the middle chamber was reduced indicating that the apparatus has concentrated the anolyte and removed iodate-periodate from the diluted wash waters. The dilute wash waters upon reaching concentration of 1.5 g./l. in the middle circulating stream were cycled through the strong base ion exchange resin resulting in complete removal of iodine and its derivatives.

EXAMPLE III The anolyte, catholyte and middle chambers of the concentration section of the apparatus were disconnected from their circulating systems by merely clamping off the hoses leading to those chambers, and the purication section of the cell was operated alone. The operating conditions and capacities with the exception of the removal of the concentration section from operation, were the same as those given in Example I. The table below shows the results of the regeneration of periodate from the spent liquors filtered from dialdehyde starch product.

Anolyte Total conc.

(Iodate- Tlm periodate) Perlodate Percent hrs. g.ll. conc., g./l. periodate Calculated as periodate.

The data show that the percent and concentration of iodate in the anolyte increase with time during the operation of the apparatus, indicating that the purification section may be operated independently of the concentration section.

EXAMPLE IV Anolyte Middle: Total Perlodate Total conc.*, cone., cone, g./l. g./l. g./l.

" Calculated as periodate.

The data indicate that the total iodate-periodate concentration of the middle chamber in the concentration section decreases with a corresponding increase in the total iodate-periodate concentration and in the periodate the concentration in relation to the length of time that the apparatus is in operation, indicating that the concentration section of the apparatus may be operated independently of the primary section.

The apparatus constructed according to this invention is suitable for the oxidation of chemically reduced per(halooxygen) acids and their salts to per(halo oxygen) acids and their salts which may be used to oxidize polysaccharides. Special application of the apparatus to the oxidation, purification and recovery of periodate and chemically reduced periodate anions which were recovered from liquors of oxidized polysaccharides, was successful.

The present invention provides a process for the purification and concentration of periodate and chemically reduced periodate anions with substantially complete recovery of all periodate and chemically reduced periodate anions by a combination of an electrolytic technique and an ion exchange technique. The present invention also provides a single electrolytic apparatus in which concentration, purification and oxidation may be carried out simultaneously.

.It is to be understood that the invention is not to be limited by these examples or by the specific reaction conditions, construction materials, concentrations of liquors and the like, but includes variations and modifications falling within the scope of the appended claim and drawings.

What is claimed is;

1. A process for the periodate oxidation of polysaccharides and the substantial recovery of periodate anions for re-use, comprising:

(a) oxidizing a polysaccharide with an aqueous to 15 weight percent solution of periodate anions to form a slurry of oxidized polysaccharide solids in a aqueous liquor containing periodate and chemically reduced periodate anions;

(b) separating the slurry solids from the primary liquor, the liquor containing less than about 5 to 15 weight percent of periodate and chemically reduced periodate anions;

(c) washing in successive steps the separated solids with water to substantially remove periodate and chemically reduced periodate anions otherwise retained by the separated solids to provide a secondary aqueous liquor containing about 1 to 8 weight percent of periodate and chemically reduced periodate, a tertiary aqueous liquor containing about 0.5 to 5 Weight percent of periodate and chemically reduced periodate and a quaternary aqueous liquor containing about 0.01 to 0.5 Weight percent of periodate and chemically reduced periodate;

(d) separating the washed solids from the aqueous liquors;

(e) drying the solids and recovering them as a dry polysaccharide product;

(f) circulating the primary and secondary liquors from a suitable anolyte reservoir as anolyte in the anolyte chamber of an electrodialytic apparatus having, in combination a two-chambered unit purification cell comprising an anolyte chamber, an anode having a surface in the anolyte chamber, a catholyte chamber, a cathode having a surface in the catholyte chamber, and a cation permselective membrane separating the chambers; a three-chamber unit concentration cell proximal the purification cell comprising an anolyte chamber, an anode having a surface in the anolyte chamber, a middle chamber, an anion permselective membrane separating the anolyte and middle chambers, a catholyte chamber, a cathode having a surface in the catholyte chamber, and a permselective membrane separating the catholyte and middle chambers, both Z-chamber and 3-charnber units being within a frame; means for circulating a common stream of primary and secondary liquors as anolyte to, through and from the anolyte chambers of the purification and concentration cells; means for circulating the tertiary liquor as electrodialysate to, through and from the middle chamber of the concentration cell; means for circulating a common stream of catholyte to, through and from the catholyte chambers of the purification and concentration cells; and means for imposing a common difference in potential across the anodes and cathodes of the purification and concentration cells; and returning the eflluent of the anolyte chamber to the anolyte reservoir;

(g) circulating the tertiary liquor from a suitable middle chamber reservoir as an electrodialysate in the middle chamber of the electrodialytic apparatus and returning said liquor to said reservoir;

(h) circulating an aqueous solution of an alkali metal hydroxide from a suitable catholyte reservoir as catholyte in the catholyte chamber of the electrodialytic apparatus and returning said catholyte to said reservoir;

(i) applying an electrical potential across the anodes and cathodes and thereby transferring by electrodialysis, periodate and chemically reduced periodate anions from the tertiary liquor electrodialysate in the middle chamber to the anolyte in the anolyte chamber through an anion permselective membrane, thereby increasing the concentration of the anolyte to about 5 to 15 weight percent periodate and chemically reduced periodate anions and reducing the concentration of the electrodialysate liquor to about 0.01 to 0.5 weight percent of periodate and chemically reduced periodate anions to form a quinary liquor said quinary liquor being returned to the middle chamber reservoir; and simultaneously oxidizing by electrolytic means the chemically reduced periodate anions in the anolyte liquor circulating in the anolyte chamber whereby an aqueous solution of about 5 to l5 Weight percent periodate anion, suitable for re-use in step (a), is formed;

(j) passing the quaternary and quinary aqueous liquors through an anion exchange resin in base form to accumulate periodate and chemically reduced periodate anions on the resin and to obtain substantially Water therefrom, the Water being suitable for re-uso in step (c); and

(k) eluting the periodate and chemically reduced periodate anions from the anion exchange resin with the basic catholyte from the catholyte reservoir, thereby regenerati-ng the resin for re-use in step (j), whereby an aqueous liquor containing periodate and chemically reduced periodate anions, suitable for use :as anolyte in step (f), is provided.

References Cited UNITED STATES PATENTS 2,713 ,5 5 3 7/ 1955 Mehltretter 204-79 2,830,941 4/ 1958 Mehltretter 204-82 3,607,694 9/1971 Heit et al. 2-04-180 P DONALD E. CZAJA, Primary Examiner M. I. MARQUIS, Assistant Examiner U.S. Cl. X.R.

gygigo y UNTTED STATES PATENT OFFICE CERTIFlCATE OF CORRECTION patent No. 3,703 ,508 Dated November 2l, 1972 Ieit et al Inventor(s) A H *I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r In the .specification column 6, line 4l, delete "motor" and substitute therefor mother column 7, linel 40, after "resin" insert in column 8, lines 21-22 delete "the resin bed M where the periodate anions are accumulated on the anion exchange resin, and the effluent"; column 8, line 53 delete "recovery and regeneration and substitute therefor resin bed where the periodate anions are accumulated on the anion exchange resin, and

the effluent -;-column 8, line 56 delete "dialysate"; and

column l2, line 43 delete "llO O" and "37 O.' in the Table and Signed and sealed this 6th day of. March 1973.

(SEAL) Attest:

EDWARD' M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

